When one number is near a hundred

I am learning to solve some addition and subtraction problems by adjusting one number to the nearest hundred.

or 301 is close to 300e.g. 198 is close to 200

Todd has $98 and saves $34 more. How much money does he have?Step1: First let’s record how much money he has in two separate piles.

$10$10$10$10$10$10$10$10$10

1 1

1 1

1 1

1

1

$10$10$10

1

1

1

1

$98 $34

Step 2: To make this question easier we change $98 into $100. We do this by taking $2 from the $34.

1

1

We now have ten $1 coins which we swap for a $10 note.

$10

So the question is now $100 plus $32

$100 $32

$100 + $32 = $132

Andy has $103 and saves $26 more. How much money does he have?Step1: First let’s record how much money he has in two separate piles.

We can also use this method for numbers just over 100.

$100 1

1

1

$10$10

1

1

1

1

1

1

Step 2: To make this question easier we change $103 into $100. We do this by moving $3 to the $26.

1

1

1

$103 $26

So the question is now $100

$100

plus $29

$29

$100 + $29 = $129

Below are the same two problems but this time I have shown how I like to record my working. You might like to do this too until you are ready to do the whole process in your head.

98 + 34 = ….

100 + 32 = …..

+2 -2

One side is getting bigger by two and one side is getting smaller by two because I am moving this amount from one pile to the other.

103 + 26 = ….

100 + 29 = …

-3 +3

129132

One side is getting smaller by three and one side is getting bigger by three because I am moving this amount from one pile to the other.

98 + 34 = …. 103 + 26 = ….

Now try these questions on your own.

Remember to first change the question then answer.

Need some more practise? Try Pg50 of Teacher Tools Addition and Subtraction Book Numeracy resources

1) 99 + 32 = ?

2) 298 + 38 = ?

3) 197 + 74 = ?

4) 301 + 27 = ?

5) 203 + 65 = ?

Click again when you have completed each question and the answer will be displayed.

100 + 31 = 131

300 + 36 = 336

200 + 71 = 271

300 + 28 = 328

200 + 68 = 268